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Grant Number: 5R01MH065252-05
Project Title: Neural Basis of Categories
PI Information: PROFESSOR EARL K. MILLER,
ekmiller@mit.edu
Abstract: DESCRIPTION: (provided by applicant)
While much is understood about neural mechanisms that analyze the
physical attributes of the visual environment, little is known about the
culmination of these analyses: the assignment of categories that give
stimuli meaning. Our group has developed a novel paradigm for studying
visual categories. A morphing system is used to blend prototypes of
"cats" and "dogs" into single images, with each image having a certain
proportion of cat vs. dog. This allows us to continuously vary shape and
precisely define a category boundary. Monkeys are trained to judge
whether two successively presented images are from the same category. We
recently found a neural correlate of category information in the
prefrontal cortex (PFC): single neurons that show a sharp change in
neural activity at the boundary between categories but relatively little
differences in activity within a category. We now plan to use this
paradigm to address fundamental questions about category
representations. Using multiple electrode techniques, we will
simultaneously record neural activity from the PFC and the inferior
temporal cortex (TIC), a visual cortical area thought to be important
for visual categories. This will allow us to directly compare and
contrast their neural properties and relative timing and thus afford a
precise assessment of the respective contributions to category-based
behaviors. We will also test for category-coding in the hippocampus, a
region that shares a close anatomical and functional relationship with
the TIC and PFC. To explore whether categorization and identification
have common neural substrates, we will record PFC and ITC activity while
monkeys switch back and forth between categorizing stimuli and
identifying individual category members. To determine if category-coding
neurons are highly specialized (like "face cells"), we will test them
with a wide range of real world stimuli. To determine whether multiple
category memberships are represented by separate neural ensembles or
instead multiplexed onto single neurons, we will record while monkeys
switch between categorizing a set of stimuli under two different
category schemes. Because categorization is central to cognition, data
from this project has the potential to impact on a wide range of
behaviors and human disorders. The ability to quickly glean concepts and
meaning from experience is disrupted in a variety of neuro psychiatric
disorders such as autism and schizophrenia. By identifying brain
structures important for these abilities, discerning their relative
roles, and uncovering their neural mechanisms, we can open a path to
drug and behavioral therapies designed to alleviate their dysfunction.
Thesaurus Terms:
brain mapping, discrimination learning, form /pattern perception,
imagery, neural information processing, neuron, neuropsychology, sensory
discrimination, stimulus /response, visual perception
brain electrical activity, cell population study, experience,
hippocampus, neuroregulation, prefrontal lobe /cortex, temporal lobe
/cortex
Macaca mulatta, computer data analysis, electroencephalography,
histology, magnetic resonance imaging, neuropsychological test,
statistics /biometry
Institution: MASSACHUSETTS INSTITUTE OF TECHNOLOGY
77 MASSACHUSETTS AVE
CAMBRIDGE, MA 02139
Fiscal Year: 2006
Department: PICOWER INSTITUTE FOR LEARNING AND MEMORY
Project Start: 01-APR-2002
Project End: 31-JAN-2007
ICD: NATIONAL INSTITUTE OF MENTAL HEALTH
IRG: IFCN
The Journal of Neurophysiology Vol. 88 No. 2 August 2002, pp. 929-941
Copyright ©2002 by the American Physiological Society
Visual Categorization and the Primate Prefrontal Cortex: Neurophysiology
and Behavior
David J. Freedman,1,2,5 Maximilian
Riesenhuber,3,4,5 Tomaso Poggio,3,4,5
and Earl K. Miller1,2,5
1Center for Learning and Memory,
2The Institute of Physical and Chemical
Research-Massachusetts Institute of Technology Neuroscience Research
Center, 3Center for Biological and
Computational Learning and 4McGovern
Institute for Brain Research, 5Department
of Brain and Cognitive Sciences, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
Subjects
Two female adult rhesus monkeys (Macacca mulatta) weighing 6.0 and 7.5
kg were used in this study. Using previously described methods (Miller
et al. 1993 ), they were implanted with a head bolt to immobilize the
head during recording and with recording chambers. Eye movements were
monitored and stored using an infrared eye-tracking system (Iscan,
Cambridge, MA). All surgeries were performed under sterile conditions
while the animals were anesthetized with isoflurane. The animals
received postoperative antibiotics and analgesics and were handled in
accord with National Institutes of Health guidelines and the
recommendations of the Massachusetts Institute of Technology Animal Care
and Use Committee.
Recording techniques
Electrode penetration sites were determined using magnetic resonance
imaging scans obtained prior to surgery. The recording chambers were
positioned stereotactically over the lateral prefrontal cortex such that
the principal sulcus and ventrolateral prefrontal cortex were readily
accessible.
Behavioral tasks
The monkeys performed a delayed match-to-category task that required
them to judge whether two successive stimuli were from the same category
(Fig. 2). The trial began when the monkey grasped a metal bar and
fixated a small (0.3°) white spot at the center of a CRT screen. They
were required to maintain gaze within a ±2° square window around the
fixation spot for the entire trial. After the initial 500 ms of
fixation, a sample image was presented at the center of the screen for
600 ms, followed by a 1,000-ms delay. Then a choice image appeared. If
the sample and choice stimuli were from the same category (a category
match), the monkeys were required to release the lever before the
stimulus disappeared 600 ms after its onset to receive a juice reward.
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